Most STIs in adolescents are asymptomatic. Recent studies in adolescents have documented relatively short periods of time until reinfection occurs (median times 4.7-7.6 months), suggesting that sexually active adolescents should be screened for STI every 6 months. Evidence-based practice is exceedingly helpful in deciding when to test, whom to test, and which methodology to use. In a recent critical analysis regarding screening women for chlamydia, screening all women for chlamydia was more cost-effective than testing only symptomatic women. With the proliferation of highly sensitive and specific assays, and the usefulness of different specimen sources (such as urine or self-swabs), health care providers of adolescents should screen all patients at risk for STIs. Although these screening and diagnostic techniques provide greater accuracy than previously attainable, screening should be part of a comprehensive methodology designed to promote good health care decisions, such as encouraging abstinence, promoting safer sexual practices, and using the most appropriate methodology to detect and treat STIs.